The field of this invention relates to a pneumatic cylinder and piston assembly, and more particular to a pneumatic cylinder and piston assembly for a weld gun device on a robotic arm.
Robotic arms have become commonplace in industrial factories for a variety of jobs. One such job is for welding metal parts together. The robotic arm that is used for welding commonly has a set of jaws for initially clamping the parts together and a weld tip which is then moved into position and welds the parts together. Pneumatic piston and cylinder assemblies have been expeditious and economical mechanisms to independently control the position of the jaws and weld tip.
The piston and cylinder assembly for the weld tip and the piston and cylinder assembly for the jaws are packaged in a common frame that is mounted on the robotic arm itself. Actuator controls for both piston and cylinder assemblies are also mounted on the robotic arm. Pneumatic piping leads from the actuator controls to the piston and cylinder assemblies. All of these components including the separate housings for the actuators, and the pneumatic piping add a significant amount of weight onto the robotic arm. The extra weight on the robotic arm provides several disadvantages. Firstly, the robotic arm must be built stronger to support the weight. Secondly, the extra weight also tends to make the arm less agile and maneuverable. Stronger and more expensive motors need to be employed to move the larger and heavier arm.
What is needed is a lightweight pneumatic piston and cylinder assembly for a robotic arm that has built-in actuators.
In accordance with one aspect of the invention, a weld gun piston and cylinder assembly has two coaxial cylinders that have a common end wall. A piston and rod are operably mounted in each respective cylinder for independently controlling a weld tip and jaws of a robotic arm. The common end wall forms a manifold with a first bore therein for receiving a spool valve. The manifold has a first set of pneumatic control passageways leading to the bore and in communication with an air supply, both ends of at least one cylinder, and an exhaust port. A spool valve is slidably mounted in the first bore for controlling the communication of the passageways in the first set with one another. A first actuator pilot valve is mounted at the side of the manifold at one end of the first bore for controlling the position of the spool valve. Preferably, the first bore is operably connected to the cylinder and piston assembly for controlling jaws of the robotic arm.
The manifold desirably has a second bore extending parallel to the first bore for receiving a second spool valve. The manifold also has a second set of pneumatic control passageways leading to the second bore and in communication with an air supply, both ends of the cylinder that controls the weld tip, and an exhaust port. The second spool valve is slidably mounted in the second bore for controlling the communication of the passageways in the second set with one another. A second actuator pilot valve is mounted at the side of the manifold at one end of the second bore for controlling the position of the second spool valve.
Preferably, the manifold has a passage leading from the respective first and second bores to the respective first and second cylinders for passing air to and from the respective cylinders at a first side of the respective pistons. The manifold has passageways leading from the respective first and second bore to first and second tubes which extend to opposing end walls of the respective first and second cylinders for passing air to and from a second side of the respective pistons.
In one embodiment, an air supply for the weld tip cylinder is in communication with an opposing end wall of the cylinder for the weld tip. A tube extends from the opposing end wall to the manifold for supplying air to the second bore and second spool valve for controlling air to the cylinder of the weld tip.
In one embodiment, a third actuator pilot valve is mounted at an opposing end of the first bore from the first actuator pilot valve to control the position of the spool valve in the opposite direction from the first actuator pilot valve. In one embodiment, the manifold has passageways leading from the air supply inlet to the actuator pilot valves mounted on the side of said manifold.
In this fashion, an efficient light weight housing contains the cylinder, pistons and rods. The housing also houses both spool valves that control the operation of the pistons and rods within the cylinders.